What is Young’s Double-Slit Experiment ? And its importance for beginners


In Quantum physics, Young’s Double-Slit Experiment is one of the most successful demonstrations that light and matter can display characteristics of both waves and particles. 

In Short :

  1. A Brief History
  2. Experiment
  3. Result
  4. Reason for the interference pattern
  5. Single Slit vs Double-Slit Experiment difference
  6.  Single Slit vs Double-Slit Experiment difference
  7. Individual particles
  8. Classical mechanics
  9. Importance
  10. Interpretations

A Brief History :

  The scientific inquiry into wave characteristics of light began in the 17th – 18th Century. Many scientists such as Robert Hooke, Christiaan Huygens, and Leonhard Euler . In 1803 Thomas Young described his famous Double-Slit Experiment which is known as Young’s Double-Slit Experiment. The Double Slit Experiment was first conducted by Thomas Young back in 1803, although Sir Isaac Newton is said to have performed a similar experiment in his own time. Newton shone a light on hair but Thomas Young did it on the slit.

Young’s Double-Slit Experiment

Experiment :

 The Double-Slit Experiment uses two coherent sources of light placed at a small distance apart. There is a screen at some distance. As the light sources turn on the interference pattern appears on the screen. The Original Double-Slit Experiment was used two-slit and one source of light. The light source was placed behind the slit. As light passes through the slit, both of them behave like point sources. 

Result :

The result of the experiment is shocking. In the screen, the light was creating bright and dark bands ( interference pattern)

Single Slit vs Double-Slit Experiment

Before knowing the reason, we need to learn what is an interference pattern. It is a phenomenon When two waves superpose to form a resultant wave of greater, lower, or the same amplitude.

 Using this phenomenon we can easily identify the characteristics of the suspect.

So in this case The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen. 

  • In Single slit experiment light spreads out in a line perpendicular to the slit.
  • In Double-Slit Experiment light diffracts when passing through a slit. The light waves interfere with each other and create a Dark and Bright band.

One of the most important versions of the experiment includes a single particle. Sending particles through double-slit one at a time resulting in a single particle on the screen. But as the experiment moves forward, the particles start to behave in wave nature and they start to create the interference pattern on the screen. This phenomenon demonstrates the wave-particle duality, which states that all matter behaves both particle and wave properties. Here the particle represents a single position and the wave represents the probability of finding the particle in a position. The phenomena have occurred with electrons, photons, some molecules, etc.

The wave pattern for electrons passing through a double slit, one-at-a-time. If you measure “which slit” the electron goes through, you destroy the quantum interference pattern shown here. However, the wave-like behavior remains so long as the electrons have a de Broglie wavelength that’s smaller than the size of the slit they’re passing through.

 In this picture, you can see the Double-Slit Experiment result of electrons. In “a” the electrons are showing their particle nature. As the experiment moves forward the wave properties can be seen. Here the high-density area represents the higher probability of finding electrons and the low electron density area represents the lower probability. \

 Most of the behavior of the light can be modeled using Classical mechanics. 

 Huygens Fresnel’s principal is one of them. In the principal, it states that each point on a wavefront generates a secondary wavelet and that the disturbance at any subsequent point can be found by summing the contributions of the individual wavelets at that point. 

The Double-Slit Experiment is one of the most successful demonstrations in Quantum mechanics. It shows that the particle has a wave nature. It also made scientists aware of the incredible, confounding world of quantum mechanics.

Interpretations :

Like  Schrödinger’s cat thought experiment, the double-slit experiment is often used to highlight the differences and similarities between the various interpretations of quantum mechanics.


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